|Mesoscale Discussion 1800|
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Mesoscale Discussion 1800
NWS Storm Prediction Center Norman OK
0618 AM CST Wed Dec 20 2017
Areas affected...Part of south-central and southeast MS and adjacent
parishes of southeast LA
Concerning...Severe potential...Watch unlikely
Valid 201218Z - 201445Z
Probability of Watch Issuance...20 percent
SUMMARY...A Marginal threat for a tornado or damaging wind gust is
possible this morning across part of south-central to southeast
Mississippi, and adjacent parishes of southeast LA.
DISCUSSION...Trends in water-vapor imagery indicated the OK
shortwave trough has moved into AR as it weakened some in amplitude.
This trough will progress east this morning into the Mid South,
while the attendant surface low shifts across northern MS into
northern AL. Given the track of the midlevel trough, the deep-layer
shear vectors with southward extent are expected to remain westerly
through the morning. This vector orientation across the
eastward-advancing cold front and lack of stronger forcing for
ascent within the warm sector suggests storm mode will remain
cellular as convection moves east of the lower MS Valley.
Strong deep-layer shear and backed southerly surface winds across
southeast LA and southern MS will sustain long hodographs with
low-level curvature. These kinematics, despite weak buoyancy,
suggest a Marginal risk for a tornado or damaging wind gust cannot
be ruled out this morning, primarily across south-central and
southeast MS, and perhaps into adjacent parishes of southeast LA.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 30789084 31499012 32118929 32218849 31278842 30838856
30518938 30508989 30539049 30619088 30789084
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